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The Food Production Chain - How Food Gets Contaminated

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It takes several steps to get food from the farm or fishery to the dining table. We call these steps the food production chain (see graphic). Contamination can occur at any point along the chain—during production, processing, distribution, or preparation.

Production

Production means growing the plants we harvest or raising the animals we use for food. Most food comes from domesticated animals and plants, and their production occurs on farms or ranches. Some foods are caught or harvested from the wild, such as some fish, mushrooms, and game.

Examples of Contamination in Production

If a hen’s reproductive organs are infected, the yolk of an egg can be contaminated in the hen before it is even laid.

If the fields are sprayed with contaminated water for irrigation, fruits and vegetables can be contaminated before harvest.

Fish in some tropical reefs may acquire a toxin from the smaller sea creatures they eat.

Processing

Processing means changing plants or animals into what we recognize and buy as food. Processing involves different steps for different kinds of foods. For produce, processing can be as simple as cleaning and sorting, or it can involve trimming, slicing, or shredding and bagging. Milk is usually processed by pasteurizing it; sometimes it is made into cheese. Nuts may be roasted, chopped, or ground (such as with peanut butter). For animals, the first step of processing is slaughter. Meat and poultry may then be cut into pieces or ground. They may also be smoked, cooked, or frozen and may be combined with other ingredients to make a sausage or entrée, such as a potpie.

Examples of Contamination in Processing

If contaminated water or ice is used to wash, pack, or chill fruits or vegetables, the contamination can spread to those items.

Peanut butter can become contaminated if roasted peanuts are stored in unclean conditions or come into contact with contaminated raw peanuts.

During the slaughter process, pathogens on an animal’s hide that came from the intestines can get into the final meat product.

Distribution

Distribution means getting food from the farm or processing plant to the consumer or a food service facility like a restaurant, cafeteria, or hospital kitchen. This step might involve transporting foods just once, such as trucking produce from a farm to the local farmers’ market. Or it might involve many stages. For instance, frozen hamburger patties might be trucked from a meat processing plant to a large supplier, stored for a few days in the supplier’s warehouse, trucked again to a local distribution facility for a restaurant chain, and finally delivered to an individual restaurant.

Examples of Contamination in Distribution

If refrigerated food is left on a loading dock for long time in warm weather, it could reach temperatures that allow bacteria to grow.

Fresh produce can be contaminated if it is loaded into a truck that was not cleaned after transporting animals or animal products.

The contents of a glass jar that breaks in transport can contaminate nearby foods.

Preparation

Preparation means getting the food ready to eat. This step may occur in the kitchen of a restaurant, home, or institution. It may involve following a complex recipe with many ingredients, simply heating and serving a food on a plate, or just opening a package and eating the food.

Examples of Contamination in Preparation

If a food worker stays on the job while he or she is sick and does not wash his or her hands carefully after using the toilet, he or she can spread pathogens by touching food.

If a cook uses a cutting board or knife to cut raw chicken and then uses the same knife or cutting board without washing it to slice tomatoes for a salad, the tomatoes can be contaminated by pathogens from the chicken.

Contamination can occur in a refrigerator if meat juices get on other items that will be eaten raw.

Mishandling at Multiple Points

Sometimes, by the time a food causes illness, it has been mishandled in several ways along the food production chain. Once contamination occurs, further mishandling of food, such as undercooking the food or leaving it out on the counter at unsafe temperatures, can make an outbreak more likely. Many pathogens grow quickly in food held at room temperature; a tiny number can grow to a large number in just a few hours. Reheating or boiling food after it has been left at room temperature for a long time does not always make it safe because some pathogens produce toxins that are not destroyed by heating.